Scientists at Rice University and the University of Colorado detail how slices of graphene in a solution arrange themselves to form a nematic liquid crystal in which particles are free-floating but aligned. If the flakes of grapheme oxide are big enough and concentrated enough, they retain their alignment as they form a gel, a handy precursor for manufacturing metamaterials or fibers with unique mechanical and electronic properties.

The team reported its discovery in the Royal Society of Chemistry journal Soft Matter. Rice authors include (left)  Matteo Pasquali, a professor of chemical and biomolecular engineering and of chemistry; James Tour (right) the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science; postdoctoral research associate Dmitry Kosynkin; and graduate students Budhadipta Dan and Natnael Behabtu. Ivan Smalyukh, (left) an assistant professor of physics at the University of Colorado at Boulder, led research for his group, in which Dan served as a visiting scientist.

"Graphene materials and fluid phases are a great research area," Pasquali said. "From the fundamental point of view, fluid phases comprising flakes are relatively unexplored, and certainly so when the flakes have important electronic properties.

"From the application standpoint, graphene and graphene oxide can be important building blocks in such areas as flexible electronics and conductive and high-strength materials, and can serve as templates for ordering plasmonic structures," he said.

ADHESIVE GRAPHENE

Recently University of Colorado measured the adhesion energy of graphene sheets, ranging from one to five atomic layers, with a glass substrate, using a pressurised "blister test" to quantify the adhesion between graphene and glass plates

Adhesion energy describes how "sticky" two things are when placed together as in Scotch tape or the gecko lizard scaling vertical walls Adhesion can also can play a detrimental role, as in suspended micromechanical structures, where adhesion can cause device failure and prolong technology, said (right) J Scott Bunch, assistant professor at the department of Mechanical Engineeering.

The first direct experimental measurements of the adhesion of graphene nanostructures, showed  "Van der Waals forces", or the sum of the attractive or repulsive forces between molecules, clamp graphene samples to the substrates and  hold together the individual graphene sheets in multilayer samples.

Researchers found the adhesion energies between graphene and the glass substrate several orders of magnitude larger than adhesion energies in typical micro-mechanical structures, an interaction they described as more liquid-like than solid-like, said Bunch.

According to him, there is great interest in exploiting graphene's incredible mechanical properties to create ultrathin membranes for energy-efficient separations as for natural gas processing and water purification, while graphene's superior electrical properties promise to revolutionise the microelectronics industry

In all of these applications, including any large-scale graphene manufacturing, the interaction that graphene has with a surface is of critical importance and a scientific understanding will help push the technology forward.

GRAPHENE INSULATOR

"So far people have never seen graphene as an insulator, unless it has been purposefully damaged, but here high-quality graphene becomes an insulator for the first time."

Two layers of boron nitrate are used not only to separate two graphene layers but also to see how graphene reacts when it is completely encapsulated by another material.

Leonid Ponomarenko, (right) the paper's lead author Ponomarenko (who carried out this work) shows his research sample: graphene quantum dots on a chip. (Courtesy: University of Manchester).

"Creating the multi-layer structure has allowed us to isolate graphene from negative influence of the environment and control graphene's electronic properties in a way it was impossible before."

"Leaving the new physics we report aside, technologically important is our demonstration that graphene encapsulated within boron nitride offers the best and most advanced platform for future graphene electronics.

It solves several nasty issues about graphene's stability and quality that were hanging for long time as dark clouds over the future road for graphene electronics.

"We did this on a small scale but the experience shows that everything with graphene can be scaled up." "It could be only a matter of several months before we have encapsulated graphene transistors with characteristics better than previously demonstrated," says Ponomarenko.

.